1. Technical Field
The present invention relates to an image forming method in which a toner image formed by a toner is transferred utilizing ultrasonic vibration, particularly related to formation of a color image formed by plural color toners, and to an image forming method employing a toner in which the dispersed state of a releasing agent is controlled to a specific condition.
2. Related Art
Recently, digital method becomes as the main stream of the image formation by the electrophotographic system. One of such the trends of the technology is a technology of full color image formation. One of the techniques to accelerate the colorization of the toner image is a full color image forming method employing an oil less toner containing a large amount of a releasing agent in the toner particle (cf. Japanese Patent Publication Open to Public Inspection, hereinafter referred to as Japanese Patent O.P.I. Publication, No. 2002-214821, paragraph [0049],). In the digital image formation, small size toner having micron order of diameter is required for visualizing a small dot image, for example, on a level of 1200 dpi (dot number per inch, 1 inch is 2.54 cm).
In such the image formation employing the small diameter toner, the transfer ability is degraded on the occasion of transfer of the image formed on the photoreceptor onto an image receiving material such as paper and OHP film. Particularly, in the formation of color image by accumulating color toners of Y, M and C, such the tendency becomes considerable and the transfer of the toner image from the photoreceptor surface or an intermediate transfer member is become instable and not reliable. Consequently, suitable color balance and the density are difficultly obtained in the color image formed on the image receiving material. Therefore, techniques have been investigated for surely transferring the toner image onto the image receiving material by applying a physical action to the photoreceptor. As one of such the measures, it is known that ultrasonic waves are applied to the carrier carrying the toner on the occasion of transference of the toner image onto the image receiving material so as to efficiently transfer the toner image from the carrier surface onto the image receiving material by the vibration of the ultrasonic waves (cf. for example, Japanese Patent O.P.I. Publication Nos. 2002-100546, paragraph [0052]–[0061] and 2001-117381, paragraph [0035] and [0062]).
However, the toner transfer methods employing ultrasonic waves disclosed in Japanese Patent O.P.I. Publication Nos. 2002-100546 and 2001-117381 are methods which have been developed for the toner which is employed while coating oil on the image receiving material on the occasion of fixing. And then results expected by the inventors cannot be obtained when the above method is applied to an image forming method employing oil-less toner.
When the transference of the oil-less toner is performed while applying the ultrasonic waves, the releasing agent is released from the toner particle by the influence of the ultrasonic waves, and then winding of the image receiving material about the fixing roller and offset are resulted.
An external additive of the oil-less toner is also released from the toner together with the releasing agent and increasing of the adhering force of the toner with the photoreceptor is resulted. Consequently, toner particles lowered in the transferring ratio are formed. And then the toner image is tend to be deformed by the vibration of the ultrasonic waves, and a problem is resulted that the toner images each having different color from each other cannot be exactly overlapped.
The invention is accomplished according to the above situation. The object of the invention is to provide an image forming method without occurrence of the winding the image receiving material about the fixing roller and the offset by employing a toner from which the releasing agent is not released when the ultrasonic waves are applied.
The invention is to provide an image forming method in which the toner image is not deformed even when the vibration of the ultrasonic waves are applied and the toner images can be exactly overlapped to form a full color image.